Dilation system and method of using the same

ABSTRACT

A method of forming an access opening through a psoas muscle to a patient&#39;s spine includes laterally inserting a stimulating dilator into the psoas muscle. The stimulating dilator has a stimulation channel formed in an outer surface thereof. An electrical pulse is transmitted via an EMG into the stimulating dilator to locate a positon of a nerve in the patient&#39;s psoas muscle. The stimulating dilator is laterally inserted through the psoas muscle and toward the patient&#39;s spine in a way that avoids the nerve. A stimulating probe is inserted into the stimulation channel along the outer surface of the stimulating dilator while transmitting an electrical pulse via the EMG into the stimulating probe to verify the position of the nerve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/202,738, filed on Jul. 6, 2016; which is a continuation of U.S.patent application Ser. No. 12/681,671, filed on Apr. 5, 2010, now U.S.Pat. No. 9,387,009, issued on Jul. 12, 2016; which is a U.S. NationalStage Entry of PCT/US08/78927, filed on Oct. 6, 2008; which claims thebenefit of U.S. Provisional Application No. 60/977,882, filed on Oct. 5,2007, entitled “ADJACENT OR LATERAL DILATOR AND METHOD OF USING THESAME;” the entire contents of each being hereby expressly incorporatedby reference herein.

BACKGROUND OF THE INVENTION

Generally speaking, sequential dilation systems enable a surgeon to makean initial incision and gradually increase the size of the incision bysequential insertion of increasingly larger dilators. Sequentialdilation is preferably able to reduce tissue damage and associatedtrauma to speed patient recovery time. In addition, dilation is utilizedto prepare a surgical path to a surgical site and a stimulator may beutilized with the dilator to direct the dilator along a path that avoidsspecific areas of the patient's anatomy, such as neural elements ornerves.

SUMMARY OF THE INVENTION

A preferred embodiment of the present invention relates generally tominimally invasive surgical procedures and apparatus and, moreparticularly, to a dilation system and related methods for directionaldilation of an incision for use in creating an access opening to apatient's spine. More specifically, the present invention relates to adilation system and related methods that are able to laterally access alumbar region of a patient's spine through the patient's psoas muscle.In accordance with one aspect of the present invention, the neuralelements or nerves of the psoas muscle are preferably mapped using astimulating probe, thereby defining a safe zone of passage. Thestimulating probe is inserted through the psoas muscle and toward orinto the intervertebral disc space. Directional dilators may be used todilate the psoas muscle to substantially separate tissue on only oneside of the stimulating probe. That is, directional, sequential dilatorsmay be inserted to dilate the psoas muscle, for example, on the anteriorside of the stimulating probe while substantially leaving the psoasmuscle intact on the posterior side of the stimulating probe.Specifically, the directional, sequential dilators may be utilized todirectionally dilate tissue away from a neural element or nerve in thepatient's body that is identified by the stimulating probe such that theneural element or nerve is not disturbed or damaged by the dilationprocess or other surgical procedures that may occur following dilation.

Alternatively, the dilation system and method may include a bluntstimulating dilator including at least one channel formed in an outersurface. The channel receives a stimulating probe that is used to mapthe neural elements or nerves of the psoas muscle and define a safe zoneof passage to the patient's spine. The stimulating dilator is insertedthrough the psoas muscle and toward or into the intervertebral discspace. A stimulating probe is then inserted into the channel formed inthe outer surface of the stimulating dilator in order to verify theneural elements or nerves.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments of the application, will be better understoodwhen read in conjunction with the appended drawings. For the purposes ofillustrating the dilation system and methods of the present application,there is shown in the drawings preferred embodiments. It should beunderstood, however, that the application is not limited to the precisearrangements and instrumentalities shown. In the drawings:

FIG. 1 illustrates a side elevational view of a dilation system inaccordance with a first preferred embodiment the present invention,which will generally be referred to herein as a directional sequentialdilation system;

FIG. 2 illustrates a magnified perspective view of the distal end of thedirectional sequential dilation system shown in FIG. 1;

FIG. 2A illustrates an exploded view of the distal end of thedirectional sequential dilation system shown in FIG. 2;

FIG. 3 illustrates a cross-sectional view of the directional sequentialdilation system of FIG. 1, taken along line 3-3 of FIG. 1;

FIG. 4 illustrates a front elevational view of the directionalsequential dilation system shown in FIG. 1 including a schematicrepresentation of a retractor that may be used in connection with thedirectional sequential dilation system;

FIG. 5A illustrates a side view of a first directional dilator used inconnection with the directional sequential dilation system shown in FIG.1;

FIG. 5B illustrates a front view of the first directional dilator shownin FIG. 5A;

FIG. 6A illustrates a side view of a second directional dilator used inconnection with the directional sequential dilation system shown in FIG.1;

FIG. 6B illustrates a front view of the second directional dilator shownin FIG. 6A;

FIG. 7 illustrates a side elevational view of a dilation system inaccordance with a second preferred embodiment of the present invention,which will generally be referred to herein as a blunt stimulatingdilation system;

FIG. 8 illustrates a top plan view of the blunt stimulating dilationsystem of FIG. 7;

FIG. 9 illustrates a magnified, top perspective view of a proximal endof the blunt stimulating dilation system of FIG. 7;

FIG. 10 illustrates a magnified bottom perspective view of a distal endof the blunt stimulating dilation system of FIG. 7;

FIG. 11 illustrates a top plan view of a dilation system in accordancewith a third preferred embodiment of the present invention, which isalso comprised of a blunt stimulating dilation system; and

FIG. 12 illustrates a magnified, top perspective view of a proximal endof the blunt stimulating dilation system of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “top” and “bottom”designate directions in the drawings to which reference is made. Thewords “inwardly” and “outwardly” refer to directions toward and awayfrom, respectively, the geometric center of the directional sequentialand blunt stimulating dilation systems and designated parts thereof. Thewords, “anterior”, “posterior”, “superior”, “inferior” and related wordsand/or phrases designate preferred positions and orientations in thehuman body to which reference is made and are not meant to be limiting.The terminology includes the above-listed words, derivatives thereof andwords of similar import.

Certain exemplary embodiments of the invention will now be describedwith reference to the drawings. In general, such embodiments relate todilation systems for accessing a patient's spinal column and,preferably, for laterally accessing the lumbar region of the patient'sspine.

As generally understood by one of ordinary skill in the art, thedilation systems will be described in connection with accessing thespine to perform a surgical procedure, but the dilation systems willfind use not only in orthopedic surgery, but in other surgicalprocedures in which a surgeon wishes to gain access to an internalcavity by cutting the skin and going through the body wall in order tokeep the incision spread apart so that surgical instruments can beinserted. For example, the dilation systems may be used for anteriorlyor posteriorly accessing the spine, for accessing the thoracic orcervical region of the spine, or for accessing nearly any other part ofthe body.

Referring to FIG. 4, generally speaking, during a lateral approach to apatient's spine 2, a psoas muscle 4, which is located on either side ofthe spine 2, is preferably separated in order to access the spine 2 and,in particular, an intervertebral disc space 6 or one or more vertebralbodies 8 within a patient's spinal column. It is desirable to avoidneural elements or nerves 9 of the lumbar plexus that lie within thepsoas muscle 4 during such procedures. The anterior third of the psoasmuscle 4 is typically considered a safe zone for muscle separation.

The neural elements or nerves 9 of the psoas muscle 4 are preferablymapped using a stimulating probe 20. In this manner, the most posteriorneural or nerve free area of the psoas muscle 4 is preferably locatedand identified. The stimulating probe 20 may then be inserted throughthe psoas muscle 4 via the most posterior neural or nerve free tissuearea or through nearly any other region that is free of neural elementsor nerves 9 and toward the spine 2 or into the intervertebral disc space6 in order to initiate safe tissue separation of the psoas muscle 4.Directional dilators 30, 40 in accordance with the first preferredembodiment of the present invention may be used to dilate the muscleseparation. In particular, the directional dilators 30, 40 may be usedto primarily separate tissue on one side of the stimulating probe 20(shown as cranial side), preferably on the anterior side of thestimulating probe 20 (e.g., the safe zone as initially identified andmarked by the stimulating probe 20). That is, by using the directionalsequential dilators 30, 40, the tissue on one side of the stimulatingprobe 20 may be moved while substantially limiting movement of thetissue on the opposite side of the stimulating probe 20. In comparison,concentric dilators separate the muscle radially and, as such, dilatetissue on both sides of the stimulating probe. This in turn may impingeon neural elements or nerves 9 located outside of the safe zone.

Referring to FIGS. 1-6B, a first preferred embodiment of a dilationsystem of the present invention is comprised of a directional sequentialdilation system 10. The directional sequential dilation system 10preferably includes a stimulating probe 20, a first directional dilator30 and a second directional dilator 40. The directional sequentialdilation system 10 may include more or less dilators such as, forexample, one, three, four, etc. The stimulating probe 20 can be anyprobe now or hereafter known for transmitting an electrical pulse. Thestimulating probe 20 preferably includes a probe tip 20 a and alongitudinal probe axis 21. The first directional dilator 30 preferablyincludes a first longitudinal axis 31, an outer surface 32, a proximalend 33, a distal end 34 and a first bore 35 extending from the proximalend 33 to the distal end 34. The first directional dilator 30 alsopreferably includes a first tip 30 a at the distal end 34 through whichthe first longitudinal axis 31 extends. The first bore 35 has a firstbore axis 36 that extends from a proximal end to a distal end of thefirst bore 35. The first longitudinal axis 36 is preferably offset orlocated a first offset distance A from the first longitudinal axis 31.The first directional dilator 30 also preferably includes a firstchannel 38 formed in the outer surface 32 thereof. The first channel 38is preferably in communication with the first bore 35 along the entirelength of the first bore 35. In use, the first bore 35 and the firstchannel 38 removably receive the stimulating probe 20 in an assembledconfiguration (e.g., when the stimulating probe 20 is slidably receivedwithin the first bore 35 of the first directional dilator 30) so that asurgeon can stimulate the first directional dilator 30. The probe axis21 of the stimulating probe 20 is preferably coaxial with the first boreaxis 36 of the first directional dilator 30 in the assembledconfiguration.

Similarly, the second directional dilator 40 preferably includes asecond longitudinal axis 41, an outer surface 42, a proximal end 43, adistal end 44 and a second bore 45 extending from the proximal end 43 tothe distal end 44. The second bore 45 preferably has a second bore axis46 that extends from the proximal end 43 to the distal end 44. Thesecond directional dilator 40 also preferably includes a second tip 40 aat the distal end 44 through which the second longitudinal axis 41extends. The second bore axis 46 of the second bore 45 is offset orlocated a second offset distance B from the second longitudinal axis 41.The outer surfaces 32, 42 of the first and second directional dilators30, 40 are preferably coated to prevent electrical leakage during use,as will be apparent to one having ordinary skill in the art. The seconddirectional dilator 40 also preferably includes a second channel 48formed in the outer surface 42 thereof that is in communication with thesecond bore 45. In use, the second bore 45 and the second channel 48receive the first directional dilator 30 therein in the assembledconfiguration (e.g., when the first directional dilator 30 is slidablyreceived within the second bore 45 of the second directional dilator40). The first longitudinal axis 31 of the first directional dilator 30is preferably coaxial with the second bore axis 46 of the seconddirectional dilator 40 when in the assembled configuration.

Because the first and second bore axes 36, 46 of the first and secondbores 35, 45 are offset from the first and second longitudinal axes 31,41 of the first and second directional dilators 30, 40, respectively,inserting the first directional dilator 30 over the stimulating probe 20and then the second directional dilator 40 over the first directionaldilator 30 causes each sequential dilator to “directionally” dilate theopening formed in the patient preferably away from any neural elements,nerves 9 or other anatomic structure on the opposite side of thestimulating probe 20, as will be described in greater detail below.

Moreover, incorporation of the first and second channels 38, 48 enablesthe first and second directional dilators 30, 40 to be more closelynested together and thus, substantially eliminate the “cookie cutter”effect that is realized when using multiple concentric dilators ofincreasing inner bore size.

The first directional dilator 30 preferably includes a plurality offirst depth indicators 37 located on the outer surface 32 thereof (asbest shown in FIGS. 5A and 5B). The plurality of first depth indicators37 extend, on the outer surface 32 of the first directional dilator 30,generally perpendicular to the first longitudinal axis 31. The pluralityof first depth indicators 37 indicate to the surgeon the variousdistances between the first tip 30 a formed at the distal end 34 of thefirst directional dilator 30 to the respective depth indicator 37 sothat, in use, the surgeon can determine how far the first directionaldilator 30 has been inserted into the patient. Similarly, as best shownin FIGS. 6A and 6B, the second directional dilator 40 preferablyincludes a plurality of second depth indicators 47 located on the outersurface 42 thereof. The plurality of second depth indicators 47 extend,on the outer surface 42 of the second directional dilator 40, generallyperpendicular to the second longitudinal axis 41. The plurality ofsecond depth indicators 47 indicate to the surgeon the various distancesbetween the second tip 40 a formed at the distal end 44 of the seconddirectional dilator 40 to the respective depth indicator 47 so that, inuse, the surgeon can determine how far the second directional dilator 40has been inserted into the patient. In the first preferred embodiment,the plurality of first and second depth indicators 37, 47 are spaced adistance of eighty millimeters (80 mm) to one hundred fifty millimeters(150 mm) from the first and second tips 30 a, 40 a in ten millimeter (10mm) increments. However, the plurality of plurality of first and seconddepth indicators 37, 47 are not limited to these dimensions and may bespaced from the first and second tips 30 a, 40 a at nearly any distanceor spacing that is preferred by a surgeon and is able to show the depththat the first and second directional dilators 30, 40 are inserted intothe patient.

In addition, the first and second directional dilators, 30, 40preferably include first and second grips 39, 49, respectively, locatedat the proximal ends 32, 42 thereof to better enable the surgeon to gripthe dilators 30, 40 in use. The first and second grips 39, 49 may beutilized by the surgeon during insertion, removal, twisting or otherwisemanipulating the first and second directional dilators 30, 40 duringsurgery.

As best shown in FIG. 1, the first directional dilator 30 preferably hasa first length Li while the second directional dilator 40 has a secondlength L2. The first length Li is preferably greater than the secondlength L2 to facilitate handling and insertion. Similarly, thestimulating probe 20 preferably has a probe length L3 such that theprobe length L3 is greater than the first length Li and the secondlength L2. The greater first length Li of the first directional dilator30 permits the proximal end 33 of the first directional dilator 30 toextend further out of the patient in the assembled and operationalconfigurations such that a surgeon may grasp the first grip 39 andremove or otherwise manipulate the first directional dilator 30 evenafter the second directional dilator 40 is inserted into the patient. Inthe first preferred embodiment, the first length is two hundred twentymillimeters (220 mm) and the second length is two hundred millimeters(200 mm), but are not so limited and may have nearly any length thatpermits insertion into the patient with the proximal ends 33, 43extending out of the patient. In addition, the first directional dilator30 preferably has a first diameter Di and the second directional dilator40 has a second diameter D2, the second diameter D2 is preferablygreater than the first diameter D1. In the first preferred embodiment,the first diameter Di is approximately seven and seven tenthsmillimeters (7.7 mm) and the second diameter D2 is approximatelyseventeen and one-half millimeters (17.5 mm). However, the first andsecond diameters Di, D2 are not so limited and may have nearly anydiameter desired by the surgeon for dilating tissue various distancesfrom the stimulating probe 20. Further, the first and second directionaldilators 30, 40 are not limited to having a circular cross-section andmay have nearly any cross-section and be adapted to shapes that permitsdirectional dilation in a manner that is preferred by a surgeon. Forexample, the first and second directional dilators 30, 40 may have anoval or oblong cross-sectional shape that urges dilation and a surgicalworking channel even further from a detected nerve 9 than a dilatorhaving a circular cross-section.

A method of using the stimulating probe 20 and first and seconddirectional dilators 30, 40 will now be described for accessing thepatient's spine 2. The technique may be particularly desirable foraccessing the lumbar region of the spine 2 via a lateral approach,although a similar or the same method may be used in other parts of thepatient's body.

Using the stimulating probe 20 and a triggered electromyograph (EMG) 50,the surgeon preferably maps a safe zone, i.e., a zone generally free ofany neural elements or nerves 9, on the tissue of interest (e.g., psoasmuscle 4). For example, on the psoas muscle 4, the anterior third of thepsoas muscle 4 is generally considered a safe zone.

Once a safe zone is established, anatomical placement is preferablyconfirmed via intra-operative fluoroscopy. The surgeon inserts thestimulating probe 20 through the psoas muscle 4 toward the patient'sspine 2. If the surgery is being performed on the intervertebral discspace 6, the distal end of the stimulating probe 20 may be inserted intothe annulus of the desired intervertebral disc space 6. Preferably, thestimulating probe 20 will be inserted via the most posterior portion ofthe safe zone.

The surgeon can insert or slide the first directional dilator 30 overthe stimulating probe 20 so that the first longitudinal axis 31 islocated to one side of the stimulating probe 20, preferably away from asensed neural element or nerve 9, through the psoas muscle 4 and into aposition proximate the patient's spine 2. The surgeon can then insertthe second directional dilator 40, if necessary, to further dilate thetissue proximate the outside surface 32 of the first directional dilator30 and further away from the sensed neural element or nerve 9. Thesurgeon can repeat this process as often as necessary. Finally, ifdesired, a retractor 60 can be inserted over the second directionaldilator 40 to subsequently retract the tissue and to permit removal ofthe first and second directional dilators 30, 40 and the stimulatingprobe 20. Alternatively, a working cannula (not shown) may be insertedover the second dilator 40 such that a procedure on the spine 2 may beperformed through the working cannula.

Additionally, if desired, before inserting the second directionaldilator 40, the stimulating probe 20 can be removed from the first bore35 and the dilator/probe combination rotated. Thereafter, using thetriggered EMG stimulation 50, the surgeon can verify that the nerve root9 is located at the expected side of the first directional dilator 30,preferably opposite the first channel 38. The stimulating probe 20 ispreferably re-inserted into the first bore 35, before insertion of thesecond directional dilator 40.

By using the first and second directional dilators 30, 40, as comparedto concentric sequential dilators as are generally known to those havingskill in the art, the directional sequential dilation system 10preferably ensures that the access opening is created away from theneural elements or nerves 9 of the psoas muscle 4, thus avoiding anyneural elements or nerves 9 that may, for example, be located on theposterior side of the stimulating probe 20. Moreover, the directionalsequential dilation system 10 also reduces the amount of tissue damagewhen separating the tissue by minimizing the amount of tissueseparation.

Alternatively, as shown in FIGS. 7-10, a one step blunt stimulatingdilator 100 comprising a second preferred embodiment of a dilationsystem of the present application may be used. The blunt stimulatingdilator 100 includes an outer surface 102, a proximal end 104, a distalend 106 and a bore 108 extending from the proximal end 104 to the distalend 106. The proximal end 104 includes an area 110 for attaching astimulating clip or cord. The distal end 106 includes an exposed,preferably pointed tip 112 for delivering electrical stimulation. Theouter surface 102 of the stimulating dilator 100 between the proximaland distal ends 104, 106 is preferably coated to prevent electricalleakage. The stimulating dilator 100 also preferably includes a channel114 formed in the outer surface 102 thereof for receiving a stimulatingprobe, such as the stimulating probe 20 illustrated in FIG. 1. Thestimulating probe can be any probe now or hereafter known fortransmitting an electrical pulse.

The stimulating dilator 100 offers the surgeon the ability tosimultaneously stimulate and dilate the psoas muscle 4. After placingthe tip 112 of the stimulating dilator 100 into the disc space, thestimulating probe 20 can be inserted through the channel 114 along theouter surface 102 of the dilator 100 to stimulate the periphery of thedilated tissue.

Alternatively, as shown in FIGS. 11 and 12, the stimulating dilator 100′comprised of a third preferred embodiment of the present application mayinclude a plurality of channels 114 formed in the outer surface 102thereof. For example, as shown, the stimulating dilator 100′ may includefour channels 114 a-d diametrically spaced on the outer surface 102 ofthe dilator 100′. In this manner, the surgeon can stimulate anterior,posterior, cranially, and caudally to verify the location of the nerveroot once the dilator 100′ is in place. Although as will be understoodby one of ordinary skill in the art, the stimulating dilator 100′ mayinclude any number of channels 114 including, for example, two, three,five or more.

A method of using the blunt stimulating dilation system will now bedescribed to produce access to the spine 2, in particular to provide anaccess opening through the psoas muscle 4 in the lumbar region of thespine 2 via a lateral approach. Although as will be understood by one ofordinary skill in the art, the method may be used in other parts of thebody and utilizing alternative approaches.

In use, a surgeon inserts, preferably laterally, the blunt stimulatingdilator 100, 100′ into the psoas 4 muscle via, for example, a twistingmotion. The surgeon preferably uses a triggered EMG 50 to transmit anelectrical pulse into the blunt stimulating dilator 100, 100′ in orderto locate a safe zone in the patient's psoas muscle 4 by locating nerveroots 9. Once the location of any nerve root 9 has been confirmed to beposterior to the blunt stimulating dilator 100, 100′, the surgeon canlaterally insert the blunt stimulating dilator 100, 100′ through thepsoas muscle 4 and toward the patient's spine 2, preferably into theannulus of the disc space 6. The surgeon inserts or slides thestimulating probe 20 into the channel 114 formed in the outer surface102 of the blunt stimulating dilator 100, 100′. If desired, the surgeonrotates the blunt stimulating dilator 100 with the stimulating probe 20located in the channel 114 while using the EMG 50 to verify the locationof the nerve root 9. Alternatively, in connection with the four channelblunt stimulating dilator 100′, rotation of the blunt stimulatingdilator 100 is not required. Rather, the stimulating probe 20 can beindependently inserted into each channel 114 a-d to verify the locationof the nerve root 9. The surgeon can then, if desired, insert aretractor over the stimulating dilator 100, 100′.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be understood that variousadditions, modifications and substitutions may be made therein withoutdeparting from the spirit and scope of the present invention as definedin the accompanying claims. In particular, it will be clear to thoseskilled in the art that the present invention may be embodied in otherspecific forms, structures, arrangements, proportions, and with otherelements, materials, and components, without departing from the spiritor essential characteristics thereof. One skilled in the art willappreciate that the invention may be used with many modifications ofstructure, arrangement, proportions, materials, and components andotherwise, used in the practice of the invention, which are particularlyadapted to specific environments and operative requirements withoutdeparting from the principles of the present invention. In addition,features described herein may be used singularly or in combination withother features. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims, and notlimited to the foregoing description.

What is claimed is:
 1. A directional sequential dilation system fordilating away from a nerve of a patient's anatomy, the directionalsequential dilation system comprising: a stimulating probe having aprobe axis; a first directional dilator including a first longitudinalaxis, a first bore having a length extending from a proximal end to adistal end of the first directional dilator and a first channel formedin an outer surface of the first directional dilator so as to be incommunication with the first bore along at least a portion of the lengthof the first bore, the first bore having a first bore axis, the firstlongitudinal axis offset from the first bore axis; and a seconddirectional dilator including a second longitudinal axis, a second borehaving a length extending from a proximal end to a distal end of thesecond directional dilator and a second channel formed in an outersurface of the second directional dilator so as to be in communicationwith the second bore along at least a portion of the length of thesecond bore, the second bore having a second bore axis, the secondlongitudinal axis offset from the second bore axis, wherein thestimulating probe is removably receivable in the first bore and thefirst directional dilator removably receivable in the second bore,wherein the stimulating probe extends into the first channel when thestimulating probe is received in the first bore, and wherein the firstdirectional dilator extends into the second channel when the firstdirectional dilator is received in the second bore.
 2. The directionalsequential dilation system of claim 1, wherein the probe axis is coaxialwith the first bore axis in an assembled configuration.
 3. Thedirectional sequential dilation system of claim 1, wherein the firstlongitudinal axis is coaxial with the second bore axis in an assembledconfiguration.
 4. The directional sequential dilation system of claim 1,further comprising: a first tip located at the distal end of the firstdirectional dilator, the first longitudinal axis passing through thefirst tip; and a second tip located at the distal end of the seconddirectional dilator, the second longitudinal axis passing through thesecond tip.
 5. The directional sequential dilation system of claim 4,further comprising: a plurality of first depth indicators located on afirst outer surface of the first directional dilator, the plurality offirst depth indicators extending on the first outer surface generallyperpendicular to the first longitudinal axis, respectively, theplurality of first depth indicators defining a plurality of firstdistances between the first tip and the plurality of first depthindicators, respectively; and a plurality of second depth indicatorslocated on a second outer surface of the second directional dilator, theplurality of second depth indicators extending on the second outersurface generally perpendicular to the second longitudinal axis,respectively, the plurality of second depth indicators defining aplurality of distances between the second tip and the plurality ofsecond depth indicators, respectively.
 6. The directional sequentialdilation system of claim 1, wherein the first and second dilatorsinclude first and second grips located at proximal ends thereof,respectively.
 7. The directional sequential dilation system of claim 1,wherein the first directional dilator has a first length and the seconddirectional dilator has a second length, the first length being greaterthan the second length.
 8. The directional sequential dilation system ofclaim 7, wherein the stimulating probe has a probe length, the probelength being greater than the first length and the second length.
 9. Thedirectional sequential dilation system of claim 1, wherein the firstdirectional dilator has a first diameter and the second directionaldilator has a second diameter, the second diameter being greater thanthe first diameter.
 10. The directional sequential dilation system ofclaim 1, wherein the first channel is radially aligned with the secondchannel when the stimulating probe is received in the first bore andwhen the first directional dilator is received in the second bore.
 11. Adirectional sequential dilation system for dilating away from a nerve ofa patient's anatomy, the directional sequential dilation systemcomprising: a stimulating probe having a probe axis; a first directionaldilator including a first longitudinal axis, a first bore having alength extending from a proximal end to a distal end of the firstdirectional dilator and a first channel formed in an outer surface ofthe first directional dilator so as to be in communication with thefirst bore along at least a portion of the length of the first bore, thefirst bore having a first bore axis, the first longitudinal axis offsetfrom the first bore axis; and a second directional dilator including asecond longitudinal axis, a second bore having a length extending from aproximal end to a distal end of the second directional dilator and asecond channel formed in an outer surface of the second directionaldilator so as to be in communication with the second bore along at leasta portion of the length of the second bore, the second bore having asecond bore axis, the second longitudinal axis offset from the secondbore axis, wherein the stimulating probe is removably receivable in thefirst bore and the first directional dilator removably receivable in thesecond bore, wherein the stimulating probe extends through the firstchannel when the stimulating probe is received in the first bore, andwherein the first directional dilator extends through the second channelwhen the first directional dilator is received in the second bore. 12.The directional sequential dilation system of claim 11, wherein theprobe axis is coaxial with the first bore axis in an assembledconfiguration.
 13. The directional sequential dilation system of claim11, wherein the first longitudinal axis is coaxial with the second boreaxis in an assembled configuration.
 14. The directional sequentialdilation system of claim 11, further comprising: a first tip located atthe distal end of the first directional dilator, the first longitudinalaxis passing through the first tip; and a second tip located at thedistal end of the second directional dilator, the second longitudinalaxis passing through the second tip.
 15. The directional sequentialdilation system of claim 14, further comprising: a plurality of firstdepth indicators located on a first outer surface of the firstdirectional dilator, the plurality of first depth indicators extendingon the first outer surface generally perpendicular to the firstlongitudinal axis, respectively, the plurality of first depth indicatorsdefining a plurality of first distances between the first tip and theplurality of first depth indicators, respectively; and a plurality ofsecond depth indicators located on a second outer surface of the seconddirectional dilator, the plurality of second depth indicators extendingon the second outer surface generally perpendicular to the secondlongitudinal axis, respectively, the plurality of second depthindicators defining a plurality of distances between the second tip andthe plurality of second depth indicators, respectively.
 16. Thedirectional sequential dilation system of claim 11, wherein the firstand second dilators include first and second grips located at proximalends thereof, respectively.
 17. The directional sequential dilationsystem of claim 11, wherein the first directional dilator has a firstlength and the second directional dilator has a second length, the firstlength being greater than the second length.
 18. The directionalsequential dilation system of claim 17, wherein the stimulating probehas a probe length, the probe length being greater than the first lengthand the second length.
 19. The directional sequential dilation system ofclaim 11, wherein the first directional dilator has a first diameter andthe second directional dilator has a second diameter, the seconddiameter being greater than the first diameter.
 20. The directionalsequential dilation system of claim 11, wherein the first channel isradially aligned with the second channel when the stimulating probe isreceived in the first bore and when the first directional dilator isreceived in the second bore.